Generally, the display devices for three-dimensional shutter glasses (3D SG) are required to include a higher screen refresh rate (generally required to be 120 Hz or 240 Hz) and the frequency of the 3D SG is 60 Hz to perform 3D effect. When a 3D signal is transmitted to the display device (such as a monitor, a projector and so on), images are alternately generated in the right or left eye in accordance with a frame sequence and transmitted wirelessly. The 3D SG receives the 3D signal and refreshes synchronously, and the corresponding images can be watched by the left and right eye and the amount of frames is kept to be the same when watching 2D images. Therefore, the different images with fast switching are watched by both eyes, and the illusion, which is an effect cannot be shot by a camcorder, is generated in the human brain and the 3D images can be seen.
FIG. 1A is an input signal polarity switching table for a pixel position in the left eye glass or the right eye glass of the 3D SG when the input signals are black and white image for the left and right. As shown in FIG. 1A, L0 and L255 respectively represent the grayscale signals for black and white images. If the L0 signal is positive polarity, the L255 signal is negative polarity and vice versa. In addition, since the voltage difference in the L0 signal is smaller, the positive and the negative voltages are close to the common voltage (V-com). Since the voltage difference in L255 signal is larger, the positive and the negative voltages are very different from the common voltage (V-com). Therefore, if the image displayed in one position of the 3D SG is always in the same polarity for a long time, as the table shown in FIG. 1A, the L255 signal keeps being positive polarity and the L0 signal keeps being negative polarity for a long period of time, charge residue similar to a direct current (DC) operation occurs in that position. It is called a 3D image sticking problem.
FIG. 1B is an input signal polarity switching table for a pixel position in the left eye glass or the right eye glass of the 3D SG for improving 3D image sticking problem. As shown in FIG. 1B, if the polarity of the image data signal is changed once every two frames, the L255 or L0 signal has both the positive and negative polarities, and the 3D image sticking problem is solved. However, when the polarity is changed once every two frames, the 3D image sticking problem is solved but another 3D images overlapping problem arises since the luminance difference sensed by the left and right eye becomes larger. As shown in FIG. 1C, since the luminance difference sensed by the left and right eye has become larger, the 3D images overlapping problem has been generated to affect the 3D display result. The luminance difference between the left and right eyes in 3D display is generated because all of the pixel charges rearranged by the share capacitance are different between odd frames and even frames in a color washout design.
Accordingly, a need has arisen to design a grayscale signal driving method to solve the 3D image sticking problem in 3D mode and the 3D image overlapping problem, which is generated when the luminance difference between the left and right eye is large.